It is well known that the use of diamond coatings offers many advantages in several fields of use. For example, diamond-coated saws and drills are used to cut concrete and steel. Drill bits coated with a thin layer of diamond may be used at much higher rotational velocities with much greater efficiency than standard drill bits. In the field of surgery, some procedures require ultra-sharp scalpels, some of which are coated with a thin diamond film. These are just a few of the many applications for diamond-coated devices.
The advantages given by diamond coating are due mainly to the physical characteristics of the diamond. Namely, diamonds exhibit low expansion when heated and-have a high degree of hardness and heat conductivity. Diamond also has a low coefficient of friction.
The deposition of thin diamond coatings, in general, has been taught by others. Typically, thin diamond films produced by the prior art are only a few Angstroms to about 1 micron thick. These teachings are disclosed in the following patents:
U.S. Pat. No. 4,842,937 issued to Meyer, et al, on Jun. 27, 1989; PA1 U.S. Pat. No. 4,988,421 issued to Drawl, et al, on Jan. 29, 1991 PA1 U.S. Pat. No. 4,992,082 issued to Drawls et al, on Feb. 12, 1991; PA1 E. P. Patent 470,644 issued to Bigelow on Feb. 12, 1992; and PA1 Japanese Patent 3,141,193 issued to Kurihara on Oct. 24, 1989.
Each of these references only teaches the formation of very thin films, with multiple thin layers being utilized to form a diamond coating of any substantial thickness. However, it is also well known that each layer that is added increases the complexity of the manufacture. Further, the composition of the different layers can vary substantially. This can be detrimental to the performance of the final diamond coating.
In order to overcome the problems inherent in producing a multiplicity of thin layers of diamond, the present inventors assisted in the development of a method of forming "thick" diamond coatings. This resulted in a process described and claimed in co-pending U.S. patent application Ser. No. 08/003,274, abandoned, filed Jan. 12, 1993, and assigned to a common assignee with the present invention. In the process described therein, glassy carbon with (or without) additives is caused to be heated in a plasma and then directed against a substrate where, by solid state transformation, the glassy carbon is converted to diamond. While this resulted in thick diamond coatings, the substrate temperature reaches temperatures in excess of 500.degree. C. because the plasma exiting the "gun" is 10,000 to 20,000 degrees, with this plasma being only about six inches from the substrate. For some applications of diamond coating, this temperature would be detrimental to the substrate.